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FOUS30 KWBC 110734
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
234 AM EST Thu Dec 11 2025

Day 1
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN
MONTANA...

...Western Washington...

The multi-day atmospheric river (A.R.) event of much of the past
week will finally conclude across western Washington today.
Northward-building ridging both at the surface and at the jet
stream level will push the remaining moisture plume from the
already weakening A.R. north into Canada, leaving much of western
Washington with residual moisture from the weakening and drying
westerly flow. Heavy rain is ongoing across much of western
Washington, roughly from Tacoma`s latitude north. CAMS guidance
shows the rain should progress a bit further south over the next
few hours as a cold front offshore pushes inland. After that it
will stall out, and the rain rates will diminish in place. Thus,
the heaviest rain over the area for this period will be over the
next few hours this morning, followed by tapering through the
afternoon and into tonight.

Record and in some areas historic flooding is ongoing from the
multiple consecutive days of heavy rain with the A.R. Comparatively
speaking, today`s rainfall totals won`t be anything near previous
days` totals. Nevertheless, the ongoing moderate to heavy rain
across northern Washington will continue to keep river levels up,
or even rising through the morning until rain rates can diminish a
bit. The Marginal Risk therefore is a compromise between the
ongoing highly impactful flooding and steady rain expected to
continue into the morning, and the fact that the second half to
two-thirds of the period should feature only light rain with the
conclusion of the A.R. event. That is to say that for all of the
Marginal Risk area, ongoing major flooding will continue through
today despite the diminishing rain, and precautions and avoidance
of flooded areas should be taken. The Marginal Risk may be able to
be dropped with the evening update.

...Northern Idaho and Far Western Montana...

Continuous steady rain is expected to continue through the entire
period across the Marginal Risk area in northern Idaho and far
western Montana today. While the A.R. is ending out west, it will
take longer to do so for Idaho and Montana as the forcings
supporting the steady rain will persist throughout the period.
Despite the heavy rain on the order of 1-2 inches over the past 24
hours, in addition to the multiple inches that fell in this same
area in days prior, impacts from flooding have been minimal across
this region. Now, with today being the tail end of the A.R., it`s
probable that if flooding impacts were to occur, they would happen
today. Thus, balancing these two offsetting factors, and in
coordination with OTX/Spokane, WA forecast office, the inherited
Slight Risk for this region was downgraded. Isolated instances of
flash flooding are still possible given the expectation of another
24 hours or so of steady rain into the west facing slopes of the
Bitterroots. However, given the lack of impacts thus far, it seems
probable that the same trends will continue through tonight. Steady
precipitation should taper off soon after the 12Z Friday end time
for the period, as an Arctic air mass further east also works to
transition any remaining rain over to snow.

Wegman

Day 2
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

Day 3
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt